1. Field of the Invention
The invention relates generally to the field of oil and gas well services. More specifically the present invention relates to a connector assembly for a perforating gun that is quick, reliable, and simple to use.
2. Description of Related Art
Perforating guns containing shaped charges are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations. These perforations hydraulically connect predetermined zones of the earth formations to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore where the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. Without perforations, the hydrocarbons entrained in the formations surrounding the wellbore could not flow into the wellbore.
Many different types of perforating guns exist, but most have the same basic components. Those components are, shaped charges, a gun tube, a gun body, a top sub or connector, a detonator, and a bottom sub. Typically the shaped charges are disposed within the gun tube, and the gun tube is inserted into the gun body. The top sub is attached to the upper portion of the gun body and connects the perforating gun to a means for raising and lowering the perforating gun into a wellbore. The bottom sub generally attaches to the lower end of the gun body. Often, the bottom sub houses the detonator within a recess located inside of its body.
When the perforating gun is situated in the portion of the wellbore where a perforation is desired, the shaped charges within the perforating gun are detonated. This in turn produces perforations through the cemented casing lining the wellbore and into the surrounding formation. As is well known in the art, each time a perforating gun is used to produce perforations inside of a wellbore, some of the components of the perforating gun are either expended or fully destroyed. Thus before perforating guns can be reused, they must be returned to the surface and refurbished to replace the parts destroyed or used up during the previous perforation. During its refurbishment the perforating gun usually must be disassembled and reassembled prior to its next deployment.
Part of the disassembly and reassembly process of the perforating gun involves disconnecting the perforating gun from its raising/lowering means; which is typically a wireline. The wireline is attachable to a cablehead, which provides the connection between the perforating gun and the wireline. Wirelines can also serve to provide a signal conduit from the surface to the perforating gun to actuate detonation of the shaped charges. Generally the wireline cablehead is affixed to the upper sub of the perforating gun and is detached during refurbishment of the perforating gun. Additionally, the upper sub is disconnected from the gun body when the expended portions of the perforating gun are replaced. Thus to help minimize the time and expense of refurbishing perforating guns between subsequent uses, it is important that disconnecting and reconnecting the upper sub to the gun body be quick, simple, and be capable of being done at or close to the wellbore.
Often, because of special or uniquely sized components used for a specific perforating application, the perforating gun must be transported to a central processing facility for refurbishment instead of the site where the perforations are performed, i.e. the field. Transportation to and from the field to a central processing facility can be financially expensive as well as costly from a lost time standpoint. On the other hand, if a perforating gun could be refurbished for reuse at a field location, the added expense and time of transportation to a central processing facility could be avoided.
Some examples of perforating guns having connection means can be found in Hromas et al., U.S. Pat. No. 6,098,716, Burleson et al. U.S. Pat. Nos. 5,778,979, 5,823,266, and 5,992,523, and Huber et al., U.S. Pat. No. 6,059,042. However each of these suffer from the drawbacks that they are complex and the connection mechanisms disclosed therein contain multiple moving parts. Additional components add complexity, which reduces reliability and adds capital and maintenance costs. Further, none of the above noted references appears to have the capability of being refurbished or modified in the field, which limits their application to single uses and reduces their flexibility of use.
Therefore, there exists a need for a device or system in connection with perforating guns that provides for a fast and simple method of connecting and disconnecting perforating guns from a wireline. Also the system should allow for the perforating guns to be prepared at a field site, provide for multiple gun lengths, minimize the time required to assemble the perforating gun assembly, and include a proven way of sealing the perforating guns from wellbore fluids.